This invention relates to direct current rotary electrical machines such as motors or generators, and more particularly to an improvement in the rectification thereof.
A direct current motor will be explained as one example of a conventional generally known direct current rotary electrical machine in reference to FIG. 1 (a developmental view of an electric circuit thereof) and FIG. 2. In the drawings, a stator having a field magnetic pole 1 comprising a permanent magnet is disposed opposite an armature 2 which is comprised of armature windings 3, an armature core 4, a commutator 5 etc., as disclosed below. The symbol P denotes a magnetic neutral plane. The armature windings 3 is provided by unit coils A lap wound a predetermined number of turns having a pair of coil sides 3a and coil ends 3P.sub.1, 3P.sub.2, 3u disposed within a slot of armature core 4. The commutator 5 is comprised of a plurality of commutator segments 5a, and two coil ends (3P.sub.1, 3P.sub.2) opposite to the pole 1 of the unit coils A of the armature windings are individually connected to two corresponding segments. A brush 6 is in rubbing contact with the commutator 5.
In the conventional machine as constructed above, when the armature winding 3 is energized through the brush 6, a current I flows to each of the coil sides 3a in the direction of the arrows and the armature 2 is rotated in direction N by the electromagnetic operation between the field flux from the permanent magnet 1 and the field flux due to the current flowing to the coil of the armature 2.
Referring to the rectification based on the unit coil (A) as shown by the solid line in FIG. 2, the current amount thereof changes between -Ic and +Ic according to the change of contact area between each of the commutator segments 5a and the brush 6 in accordance with the revolution of the armature 2.
Here, the reference symbol P shows the timing point where each of a pair of coil sides 3a is positioned on a magnetic neutral plane. Ideally, it is desirable that the current value be in the vicinity of zero at this point P as shown by the dashed line in FIG. 2. However, primarily because of such factors as the self inductance of the unit coils A, in reality this is delayed as shown by the solid line in FIG. 2 so that the torque and output characteristics, etc. are reduced.
So, in the related art, the position of the brush 6 in relation to the field magnetic pole is shifted, for example, as depicted by the dotted line of FIG. 1. This results in the following demerits. Namely, since the direction of shift of the brush etc. in relation to the field magnetic pole differs according to such factors as the direction of rotation of the armature, or whether the machine is a motor or a generator, two kinds of fixing members holding the brush etc. must be prepared in accordance with the direction of shift of the brush 6 and the two types cannot be used in place of one another and further, if an interchangeable part is attempted to be manufactured it would have to be increased in size due to problems with the positional relation with other parts resulting in the demerit that the machine becomes large in size.